Physics is exciting in many ways. To some people the excitement comes from the elegance and universality of its basic theories, from the fact that
a few basic concepts and laws can explain phenomena covering a large range of magnitude of physical quantities. To some others, the challenge in carrying out imaginative new experiments to unlock the secrets of nature, to verify or refute theories, is thrilling. Applied physics is equally demanding. Application and exploitation of physical laws to make useful devices is the most interesting and exciting part and requires great
ingenuity and persistence of effort.
What lies behind the phenomenal progress of physics in the last few centuries? Great progress usually accompanies changes in our basic perceptions. First, it was realised that for scientific progress, only qualitative thinking,though no doubt important, is not enough.Quantitative measurement is central to the growth of science, especially physics, because
the laws of nature happen to be expressible in precise mathematical equations.
The second most important insight was that the basic laws of physics are universal - the same laws apply in widely different contexts. Lastly, the strategy of approximation turned out to be very
successful. Most observed phenomena in daily life are rather complicated manifestations of the basic laws.
Scientists recognised the importance
of extracting the essential features of a
phenomenon from its less significant aspects.
It is not practical to take into account all the complexities of a phenomenon in one go. A good strategy is to focus first on the essential features, discover the basic principles and then introduce corrections to build a more refined theory of the phenomenon. For example, a stone and a feather
dropped from the same height do not reach the ground at the same time. The reason is that the essential aspect of the phenomenon, namely free
fall under gravity, is complicated by the presence of air resistance. To get the law of free fall under gravity, it is better to create a situation wherein the air resistance is negligible. We can, for example, let the stone and the feather fall through a long evacuated tube.
In that case, the two objects will fall almost at the same rate, giving the basic law that acceleration due to gravity is independent of the mass of the object. With the basic law thus found, we can go back to the feather, introduce corrections due to air resistance, modify the existing theory and try to build a more realistictheory of objects falling to the earth under
gravity.
Hypothesis, axioms and models
One should not think that everything can be proved with physics and mathematics. All physics, and also
mathematics, is based on assumptions, each of which is variously called a hypothesis or axiom or postulate, etc.
For example, the universal law of gravitation proposed by Newton is an assumption or hypothesis, which he proposed out of his ingenuity. Before him,there were several observations, experiments and data, on the motion of planets around the sun, motion of the moon around the earth, pendulums, bodies falling towards the earth etc. Each of these required a separate explanation, which was more
or less qualitative.
What the universal law of gravitation says is that, if we assume that any two bodies in the universe attract each other with a
force proportional to the product of their masses and inversely proportional to the square of the
distance between them, then we can explain all these observations in one stroke. It not only explains these phenomena, it also allows us to predict the results of future experiments.
A hypothesis is a supposition without assuming that it is true. It would not be fair to ask anybody to prove the universal law of gravitation, because
it cannot be proved. It can be verified and substantiated by experiments and observations.
